The idle musings of a former military man, former computer geek, medically retired pastor and now full-time writer. Contents guaranteed to offend the politically correct and anal-retentive from time to time. My approach to life is that it should be taken with a large helping of laughter, and sufficient firepower to keep it tamed!

Tuesday, April 17, 2018

Can "quantum radar" expose stealth aircraft?

Researchers at the University of Waterloo are developing a new technology that promises to help radar operators cut through heavy background noise and isolate objects —including stealth aircraft and missiles— with unparalleled accuracy.

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Stealth aircraft rely on special paint and body design to absorb and deflect radio waves—making them invisible to traditional radar. They also use electronic jamming to swamp detectors with artificial noise. With quantum radar, in theory, these planes will not only be exposed, but also unaware they have been detected.

Quantum radar uses a sensing technique called quantum illumination to detect and receive information about an object. At its core, it leverages the quantum principle of entanglement, where two photons form a connected, or entangled, pair.

The method works by sending one of the photons to a distant object, while retaining the other member of the pair. Photons in the return signal are checked for telltale signatures of entanglement, allowing photons from the noisy environmental background to be discarded. This can greatly improve the radar signal-to-noise in certain situations.

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“This project will allow us to develop the technology to help move quantum radar from the lab to the field,” said Baugh. “It could change the way we think about national security.”

Quantum computing is another area of great importance, one in which the USA and its allies appear to be falling far behind. China has announced that it will invest $10 billion into research in that field, vastly more than we are currently doing. It wants to "build a quantum computer with a million times the computing power of all others presently in the world". That's quite an ambition: but if they throw enough money and engineers at the project, they may well succeed. That poses a grave threat to the security of all encrypted or encoded signals and information. As The Hill recently pointed out, "It puts in jeopardy our entire military and national ability to keep our secrets, well, secret. Today’s strongest encryption could be broken in a matter of seconds."

China is also putting tremendous effort into developing quantum radar systems, that it claims can detect so-called "stealthy" aircraft. The Canadian research referred to above is a drop in the bucket, funding-wise, compared to what China is spending. I suspect the "stealth advantage" claimed by the USAF may not be an advantage for much longer. If "quantum radar" becomes a reality, the service's current emphasis on stealth fighter and strike aircraft (the F-22 and F-35 respectively) will be severely compromised. In contrast, the US Navy, which has continued to buy conventional, non-stealthy aircraft in large numbers even as it prepares to field the stealthy F-35C, will be not much worse off. It'll still rely on tactics, skill and electronic warfare to get its strikes through (as does the Israeli Air Force). It won't have all its eggs in one (suddenly non-stealthy) basket.

As a career radio designer who spent his last few working years working as a radar designer, my first thought was "is this an April Fool's day article?"

Let's ignore the radar aspect and talk about quantum computers. Did you know that there is serious academic debate on whether anything built so far is actually a quantum computer? Yet D-Wave is selling these horrendously expensive systems as quantum computers that nobody can prove are quantum computers?

What an ideal market for hucksters.

Why not take it apart and probe it? Or why not run a sample computation, a benchmark if you will, on it and another computer to see which is faster. Unfortunately, it's not that easy. It violates the laws of quantum physics to be able to look inside (probe it), so the system can't be probed. When a quantum system is observed, it collapses to one state or the other. It ceases to be a quantum computer.

Even if there were a speedup, it would be hard to measure. There was a good deal of hype about an experiment last year by a scientist whom D-Wave had hired as a consultant, showing that the D-Wave 2 did a certain calculation 3,600 times faster than a conventional machine. But as it turned out, the likelier reason the conventional computer was slow was that its software was slow. Other researchers said they’d been able to make an ordinary laptop, using different software, run as fast as the D-Wave.

Why is anybody mentioning encryption in these comments. That article is about detection, which doesn't use encryption.

This is the first time I've seen the words "radar" and "photon" in the same sentence. Radar uses radio waves, not the much much shorter wavelength electromagnetic waves we call "light". So do some physicists have a photonic theory of radio waves, as they do for "light" wavelengths?- Bart Noir

The entire electromagnetic spectrum from ELF radio up to gamma rays is all photons. Just different frequencies. I mentioned encryption because the post mentioned encryption. The rest of it is a Black Art to me.

It seems that this would only work where the stealth is incomplete. You'd have to receive some photons reflected from the stealth aircraft. If you didn't receive any, a single radar could not tell if it was perfect absorption or clear air.

Distributed arrays of transmitters and receivers can already detect stealth aircraft, because they create a hole.

I suppose that stealth absorption cannot be perfect, and any amount of radar reflection, even very small, would be enough to let this quantum radar detect objects. Because if it finds one of its entangled photons, it had to come back from something. I think there'd still be a major problem with false readings from birds and dust.

Can't work, not even theoretically. When the photons reflect off the plane, they are interacting with the surface molecules. The quantum waveform collapses, and is no longer entangled. Spin is conserved, but that can happen in any number of ways. What usually happens is that the spin of the target and the photon are both altered in opposite directions.

Oh, and how, exactly, are the return streams going to be compared to the baseline streams? You can only check them once, then the baseline is corrupted (by definition). You can't synch them, because if you do, the radar would only work against stationary objects at a specific, fixed distance.

Read a article about how the Australians tracked B-2's. Evidently they could not get any type of return from the plane, but were able to get a return from the disturbed air that the B-2's were creating. I think it was a very specialized type of long range weather radar and it was getting anomalies that when someone at the RAAF was notified and did further work and they figured it out.

Interesting. I seem to remember reading an article a few years ago about a "passive radar system that would be able to defeat stealth technology. The idea as I seem to recall was to use multiple radio wave detectors in an urban environment to paint a picture of normal background signals from TV, Radio, Cellular towers etc. The idea was that any object moving through said space would disrupt the normal signals bouncing off rooftops, building etc in such a way that would allow the stealth aircraft to be detected. Never heard anything about this approach since though.